Composite Modelling of the Interactions Between Beaches and Structures (CoMIBBS)
CoMIBBS is a Joint Research Activity within the EC Framework 6 Integrated Infrastructure Initiative, HYDRALAB-III. Details can be found in the sections below or by contacting the JRA coordinator (see right).
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Aims and objectives
The aim of CoMIBBS is to improve the service provided by hydraulic laboratories by developing techniques and good practice guidelines for composite modelling, which is the integrated and balanced use of physical and numerical models. Composite modelling techniques will be developed and tested for four generic types of seabed / fluid / structure interactions. A set of practical guidelines will be produced, detailing the composite modelling techniques tested during the project.
The main objectives of CoMIBBS are to:
- Analyse the functionality of physical and numerical models and to outline the composite modelling approaches to be evaluated.
- Investigate the optimum choice of models for addressing generic problems of seabed / structure interaction.
- Produce guidelines on the strengths and weaknesses of a range of physical and numerical models.
- Produce best practice guidelines on composite modelling techniques of the interactions between beaches and structures.
State of the art
Hydraulic studies have been traditionally undertaken with physical models, which reproduce flow phenomena at reduced scale with dynamic similarity. Today, numerical models are increasingly being used in place of physical models. These models rely on mathematical descriptions of complex turbulent processes and boundary conditions but can be cheap and versatile. Physical and numerical models both have their strengths and weaknesses (van Os et al, 2004, J Hyd. Res. 42[4] 341-356, Table 2) and their merits must be compared to the benefits of theoretical analysis (desk studies) and measurements made in the field.
A single tool can not adequately reproduce the complex processes involved in coastal problems and thus replace all the others. Combining tools can add value, but also cost. In most cases the boundary conditions for a physical model come from a regional, numerical model. The models are run in sequence from large scale to small scale and frequently all the runs of one model are completed before the next (smaller area) model is run. Compromises are made with the validity of the models and about the (limited) amount of information that is transferred from one model to another. In the infrequent occasions when physical and numerical models of the same structure and beach are run, differences in the results are normally seen. The differences may be due to a number of factors, such as the poor description or parameterisation of processes in the numerical model, the use of simplified boundary conditions or idealised structures (possibly as designed, rather than as exists) in physical and numerical models. It is not always possible to decide which error is most important and to decide which model to believe.
Advances through development of composite modelling
CoMIBBS will devise, test and evaluate new methods of composite modelling, showing how physical and numerical models can be used together in a balanced approach. It will describe limitations on the applicability of physical and numerical models. It will produce best practice guidelines on composite modelling techniques. It is anticipated that these guidelines will be used by a much wider modelling community than just the HYDRALAB participants.